The present invention concerns appliances of the vacuum cleaner type for picking up dirt, dust, debris, etc., referred to generally herein as “waste”. More particularly, the invention relates to vacuum cleaners that separate the waste from the suction air by centrifuging.
The present invention is directed particularly to improvements in waste separation devices using a generally cylindrical separation chamber, in which air is caused to rotate and exits the chamber through openings provided in a conduit at the center of the chamber.
French patent document 2 786 682, incorporated herein by reference, describes such an appliance having a central conduit is provided at its periphery with a multitude of holes having substantially radially extending axes. A tank for recovering the waste is disposed under the central conduit and closes the separation chamber.
Thus, when the main suction group is in operation, the waste on the floor being cleaned is suctioned with the aid of a conduit that generally terminates in a nozzle and is connected to the separation chamber. The air flow loaded with waste then penetrates to the interior of the separation chamber along a tangential direction.
The heavier waste pieces, or particles, are then separated from the main air flow, by centrifuging, and also by the barrier constituted by the conduit provided with holes. These waste particles then fall into the recovery tank.
International application WO 03/047412, incorporated herein by reference, describes a waste separation device comprising an air inlet conduit opening along a tangential direction into a waste separation chamber defining an internal volume having substantially the form of a cylinder.
According to one of the particularities of this device, the cylindrical separation chamber has a separation screen, which is also cylindrical, in the central part of the chamber. This screen separates the chamber from a conduit connected to the suction group, which conduit has, in particular, a filtration group.
The chamber has, moreover, a channel for evacuation of the waste in a radial direction. The channel is coupled to a sealed tank for collecting the centrifuged waste. This channel can also extend in a tangential direction.
In a manner analogous to the description in the document previously described, when the main suction group is placed in operation, the air flow loaded with waste penetrates to the interior of the separation chamber with a high speed obtained by the dimensional configuration of the different parts of the device, and particularly the small passage cross section at the level of the separation chamber.
The heaviest waste particles are then separated from the main air flow by centrifuging and also by the action of the cylindrical screen. They then penetrate into the sealed tank via the evacuation channel.
Such a device produces a relatively good separation of waste, taking into account the high speed of the air in the separation chamber and the fact that the suctioned air, penetrating into the chamber in a direction tangential to the cylindrical screen, must pass through openings provided in the screen, which implies a change in direction close to 90° on average.
Improvements in the above-described separation device are disclosed in the Japanese patent document 11290724 in which, according to one of the embodiments, the holes in the central conduit are masked by walls in the form of quarters of a sphere.
FIGS. 1, 2a and 2b herein illustrate the progress in this art. FIG. 1 shows the principle of a chamber for separation by centrifuging, in which the air enters tangentially into a separation chamber 2 and is forced to penetrate into a multitude of openings formed in a central conduit 6. The separated waste particles 8 then drop into a tank 10.
FIG. 2a shows an air trajectory by a solid line and a waste particle trajectory with a dotted line at the level of an opening 4 of the separator shown in FIG. 1. As shown in this Figure, air penetrates into opening 4 by having its trajectory deflected through an angle of around 90°. The heavier particles, as a result of their velocity, cannot change the direction of their trajectory. In addition, by the centrifugal effect, these particles are displaced toward the periphery of the cylindrical separation chamber, from which they are recovered in tank 10.
Certain particles, and particularly those that are lightest, remain close to openings 4 and can pass through these openings by slightly changing their trajectory, as shown by the dotted line in FIG. 2a. 
Thus, the performance of such a separator is limited by this phenomenon since the smallest particles are poorly separated.
FIG. 2b shows the proposed improvement provided by the device according to one of the embodiments disclosed in the Japanese patent document 11290724. According to this simplified diagram, the device has walls 12 in the form of a quarter of a sphere masking openings 41 in the direction of circular movement of the air. These walls cause the finest particles to be oriented toward the periphery of the separation chamber and to thus follow a trajectory that distances them from the openings, as represented by the dotted line. Overall, the separation power of the device is improved.
However, the trajectory of the entraining air must follow a more tortuous path in order to enter into openings 41 since this requires that the trajectory of the air be deflected by around 180° in order to enter into conduit 6, as shown by the solid line in FIG. 2b. This results in supplementary pressure drops, thereby requiring more powerful, and thus more costly, suction sources.
Moreover, the form of wall 12, which extends, at its base, at a right angle to conduit 6, generates turbulence phenomena t that affect the separation of the particles. It is feared that this can create dust accumulation zones that can become sources for the development of undesired bacteria.